We found this circuit in a 1998 publication. The circuit has controls for both frequency and signal strength. A lamp is used to monitor the signals. The supply is made with a voltage of 12 V.
This circuit, found in a 1997 publication, activates a lamp or a monitoring camera when the bell...
This circuit is from a 1967 Triplett manual. The circuit uses components of the time, the common...
The TDA1521A is compatible in pinout with the TDA1521 and contains the same crystal, but it is...